1. Field of the Invention
The present invention relates to an organic electro-luminescence (EL) element for a display device and, more particularly, to an encapsulation of an organic EL element for a display device.
2. Description of the Related Art
In an electro-luminescence (EL) element used for a display device, electric current applied to specific fluorescence or phosphorus transforms electricity into luminosity. Based on the materials utilized in a luminescent layer, EL elements are classified into organic and inorganic, wherein the organic EL element employs laminated organic layers having advantages such as thin profile, light-weight, high luminescent efficiency, and low driving voltage. Moreover, based on the materials utilized in an organic luminescent layer, the organic EL elements are classified into molecule-based devices and polymer-based devices. The molecule-based device employs dyes or pigments to form an organic luminescent layer called an organic light emitting display (OLED) The polymer-based device employs conjugate macromolecule to form an organic luminescent layer called a polymer light emitting display (PLED).
In order to prevent the internal space of an organic EL element from developing high humidity, a sealing case is commonly used to package a glass substrate on which metal electrodes and one or more organic luminescent layers are formed. Also, in order to prolong the active lifetime, a desiccant is provided to absorb moisture and impurities generated in the interior space, the water and oxygen permeating from the atmosphere, and the moisture generated from the outgassing effect caused by the bonding agent on the rim of the sealing case. Furthermore, various technologies for reducing interior humidity have been developed to eliminate dark spots, such as forming photo-hardened resin on the glass substrate, plating a metal oxide, fluoride or sulfide on the glass substrate, forming a water-resistant film on the glass substrate, and using an airtight case to package the organic EL element. Nevertheless, other problems, such as leakage current, crosstalk and oxide dissolution, remain to be solved.
As shown in FIG. 1, U.S. Pat. No. 5,882,761 discloses an encapsulation 1 of an organic EL element, which comprises a glass substrate 10, a sealing agent 9 composed of a UV-cured resin formed on the rim of the glass substrate 10, and a sealing case 7 bonded to the glass substrate 10 by the sealing agent 9. Thus, an internal space 11 formed by the glass substrate 10 and the sealing case 7 becomes an airtight space. In the airtight space, a lamination body 6 formed on the glass substrate 10 comprises an anode layer 3, an organic luminescent material layer 4, and a cathode layer 5. A drying substance 8 may be disposed on the bottom of the sealing case 7 and separated from the lamination body 6 by an internal space 11 filled with dried inert gas. The drying substance 8 comprises a solid compound, such as BaO, CaO, CaSO4, and CaCl2, which chemically absorbs moisture and remains in solid state. The drying substance 8 is a sheet body fixed on the concave of the sealing case 7 via bonding.
To provide an attachment area for the drying substance 8, however, the fabrication of the sealing case 7 having a concave bottom necessitates an all-in-one technology, which may encounter problems, such as shaping difficulties, high process costs, and a difficult in applying to glass materials. Also, as the depth of the concave of the sealing case 7 increases, the volume of the internal space 11 increases to provide a larger space for accommodating moisture and oxygen, resulting in an uncertainty of the moisture-absorbing effectiveness provided by the drying substance 8. Moreover, the design of the sealing case 7 having a concave will unfavorably increase the thickness of the encapsulation structure, which does not conform to the development trend toward light-weight, thin profile and small size characteristics of the panel display.
The present invention provides an encapsulation of an organic electro-luminescence element for a display device and a method for encapsulating the same to solve the problems accompanied by the prior art.
In an encapsulation of an organic electro-luminescence element for a display device, a luminescent body is formed on the inner surface of a first substrate. A second substrate serves as a planar sealing case. A sealing agent is formed on the rims of the first substrate and the second substrate to bond the first substrate and the second substrate and form an airtight space. A first drying layer is formed on the inner surface of the second substrate within the airtight space.
Accordingly, it is an object of the invention to form the drying layer on the planar sealing case by sputtering to simplify the encapsulating process.
It is another object of the invention to form the drying layer on the planar sealing case by sputtering to reduce process cost of the sealing case.
Yet another object of the invention is to form the drying layer on the planar sealing case by sputtering to increase material selectivity of the sealing case.
It is a further object of the invention to provide a combination of the sealing case having a planar profile and the drying layer with an extremely thin deposition, resulting in a smaller volume of the internal space 32 as compared with the prior art.
These and other objects and advantages of the present invention will become readily apparent upon further reference to the following detailed description and the accompanying drawings.